German Patent Application No. 44 14 022 A1 describes a chassis equipped with an active suspension system between the wheels and the body of the vehicle. The suspension system has a passive spring element assigned to each wheel and an active, controllable supporting unit on which the spring element is supported and whose stroke position can be adjusted with the help of a hydraulic displacement unit.
To control the supporting units, first the stroke positions of the supporting units are detected by displacement sensors, and the actual supporting forces acting between the wheels and the body of the vehicle are determined from the stroke positions in an electronic controller according to a linear relationship. The supporting forces are compared in the electronic controller with predetermined setpoint supporting forces calculated from setpoint stroke positions. The control deviation then results in a control signal to adjust the supporting units.
With this device and this method, it is possible to adjust the desired supporting forces directly by displacement measurements. However, German Patent Application No. 44 14 022 A1 does not describe other possible uses.
German Patent Application No. 41 17 897 A1 describes a control concept for damping the stroke, pitch and roll motions of a chassis. This concept, which also permits adjustment of the roll torque distribution between the front and rear axles as an additional degree of freedom of the "chassis" system, is based on a variant of skyhook damping, as a result of which a controlling force, which depends on the rate of buildup, is determined. To perform the control, vertical buildup rates must first be determined at selected locations on the chassis. The vertical buildup rates are then used to calculate the rates of stroke, roll and pitch, which are then converted to quasi-modal rates from which setpoint forces for actively adjustable hydraulic cylinders are determined.
The control concept known from German Patent Application No. 41 17 897 A1 is capable of influencing a majority of degrees of freedom of the system. However, several control matrices with a plurality of coefficients are needed for the control concept due to its complexity. Further, any determination of optimal coefficient values will be of great expense. Another disadvantage is that any buildup rates must be measured by sensors and the measurement of the buildup rates are more complicated that measurement of simple changes in position.